1 // Copyright 2018 The Abseil Authors.
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
7 // https://www.apache.org/licenses/LICENSE-2.0
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
15 #ifndef ABSL_HASH_HASH_TESTING_H_
16 #define ABSL_HASH_HASH_TESTING_H_
18 #include <initializer_list>
20 #include <type_traits>
23 #include "gmock/gmock.h"
24 #include "gtest/gtest.h"
25 #include "absl/hash/internal/spy_hash_state.h"
26 #include "absl/meta/type_traits.h"
27 #include "absl/strings/str_cat.h"
28 #include "absl/types/variant.h"
32 // Run the absl::Hash algorithm over all the elements passed in and verify that
33 // their hash expansion is congruent with their `==` operator.
35 // It is used in conjunction with EXPECT_TRUE. Failures will output information
36 // on what requirement failed and on which objects.
38 // Users should pass a collection of types as either an initializer list or a
39 // container of cases.
41 // EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(
42 // {v1, v2, ..., vN}));
44 // std::vector<MyType> cases;
46 // EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(cases));
48 // Users can pass a variety of types for testing heterogeneous lookup with
51 // EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(
52 // std::make_tuple(v1, v2, ..., vN)));
55 // Ideally, the values passed should provide enough coverage of the `==`
56 // operator and the AbslHashValue implementations.
57 // For dynamically sized types, the empty state should usually be included in
60 // The function accepts an optional comparator function, in case that `==` is
61 // not enough for the values provided.
65 // EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly(
66 // std::make_tuple(v1, v2, ..., vN), MyCustomEq{}));
68 // It checks the following requirements:
69 // 1. The expansion for a value is deterministic.
70 // 2. For any two objects `a` and `b` in the sequence, if `a == b` evaluates
71 // to true, then their hash expansion must be equal.
72 // 3. If `a == b` evaluates to false their hash expansion must be unequal.
73 // 4. If `a == b` evaluates to false neither hash expansion can be a
74 // suffix of the other.
75 // 5. AbslHashValue overloads should not be called by the user. They are only
76 // meant to be called by the framework. Users should call H::combine() and
77 // H::combine_contiguous().
78 // 6. No moved-from instance of the hash state is used in the implementation
81 // The values do not have to have the same type. This can be useful for
82 // equivalent types that support heterogeneous lookup.
84 // A possible reason for breaking (2) is combining state in the hash expansion
85 // that was not used in `==`.
90 // template <typename H>
91 // friend H AbslHashValue(H state, Bad2 x) {
93 // return H::combine(std::move(state), x.a, x.b);
95 // friend bool operator==(Bad2 x, Bad2 y) {
101 // As for (3), breaking this usually means that there is state being passed to
102 // the `==` operator that is not used in the hash expansion.
107 // template <typename H>
108 // friend H AbslHashValue(H state, Bad3 x) {
110 // return H::combine(std::move(state), x.a);
112 // friend bool operator==(Bad3 x, Bad3 y) {
114 // return x.a == y.a && x.b == y.b;
118 // Finally, a common way to break 4 is by combining dynamic ranges without
119 // combining the size of the range.
124 // template <typename H>
125 // friend H AbslHashValue(H state, Bad4 x) {
126 // return H::combine_contiguous(std::move(state), x.p, x.p + x.size);
128 // friend bool operator==(Bad4 x, Bad4 y) {
129 // // Compare two ranges for equality. C++14 code can instead use std::equal.
130 // return absl::equal(x.p, x.p + x.size, y.p, y.p + y.size);
134 // An easy solution to this is to combine the size after combining the range,
136 // template <typename H>
137 // friend H AbslHashValue(H state, Bad4 x) {
138 // return H::combine(
139 // H::combine_contiguous(std::move(state), x.p, x.p + x.size), x.size);
142 template <int&... ExplicitBarrier, typename Container>
143 ABSL_MUST_USE_RESULT testing::AssertionResult
144 VerifyTypeImplementsAbslHashCorrectly(const Container& values);
146 template <int&... ExplicitBarrier, typename Container, typename Eq>
147 ABSL_MUST_USE_RESULT testing::AssertionResult
148 VerifyTypeImplementsAbslHashCorrectly(const Container& values, Eq equals);
150 template <int&..., typename T>
151 ABSL_MUST_USE_RESULT testing::AssertionResult
152 VerifyTypeImplementsAbslHashCorrectly(std::initializer_list<T> values);
154 template <int&..., typename T, typename Eq>
155 ABSL_MUST_USE_RESULT testing::AssertionResult
156 VerifyTypeImplementsAbslHashCorrectly(std::initializer_list<T> values,
159 namespace hash_internal {
161 struct PrintVisitor {
163 template <typename T>
164 std::string operator()(const T* value) const {
165 return absl::StrCat("#", index, "(", testing::PrintToString(*value), ")");
169 template <typename Eq>
172 template <typename T, typename U>
173 bool operator()(const T* t, const U* u) const {
178 struct ExpandVisitor {
179 template <typename T>
180 SpyHashState operator()(const T* value) const {
181 return SpyHashState::combine(SpyHashState(), *value);
185 template <typename Container, typename Eq>
186 ABSL_MUST_USE_RESULT testing::AssertionResult
187 VerifyTypeImplementsAbslHashCorrectly(const Container& values, Eq equals) {
188 using V = typename Container::value_type;
193 std::string ToString() const {
194 return absl::visit(PrintVisitor{index}, value);
196 SpyHashState expand() const { return absl::visit(ExpandVisitor{}, value); }
199 using EqClass = std::vector<Info>;
200 std::vector<EqClass> classes;
202 // Gather the values in equivalence classes.
204 for (const auto& value : values) {
205 EqClass* c = nullptr;
206 for (auto& eqclass : classes) {
207 if (absl::visit(EqVisitor<Eq>{equals}, value, eqclass[0].value)) {
213 classes.emplace_back();
216 c->push_back({value, i});
219 // Verify potential errors captured by SpyHashState.
220 if (auto error = c->back().expand().error()) {
221 return testing::AssertionFailure() << *error;
225 if (classes.size() < 2) {
226 return testing::AssertionFailure()
227 << "At least two equivalence classes are expected.";
230 // We assume that equality is correctly implemented.
231 // Now we verify that AbslHashValue is also correctly implemented.
233 for (const auto& c : classes) {
234 // All elements of the equivalence class must have the same hash
236 const SpyHashState expected = c[0].expand();
237 for (const Info& v : c) {
238 if (v.expand() != v.expand()) {
239 return testing::AssertionFailure()
240 << "Hash expansion for " << v.ToString()
241 << " is non-deterministic.";
243 if (v.expand() != expected) {
244 return testing::AssertionFailure()
245 << "Values " << c[0].ToString() << " and " << v.ToString()
246 << " evaluate as equal but have an unequal hash expansion.";
250 // Elements from other classes must have different hash expansion.
251 for (const auto& c2 : classes) {
252 if (&c == &c2) continue;
253 const SpyHashState c2_hash = c2[0].expand();
254 switch (SpyHashState::Compare(expected, c2_hash)) {
255 case SpyHashState::CompareResult::kEqual:
256 return testing::AssertionFailure()
257 << "Values " << c[0].ToString() << " and " << c2[0].ToString()
258 << " evaluate as unequal but have an equal hash expansion.";
259 case SpyHashState::CompareResult::kBSuffixA:
260 return testing::AssertionFailure()
261 << "Hash expansion of " << c2[0].ToString()
262 << " is a suffix of the hash expansion of " << c[0].ToString()
264 case SpyHashState::CompareResult::kASuffixB:
265 return testing::AssertionFailure()
266 << "Hash expansion of " << c[0].ToString()
267 << " is a suffix of the hash expansion of " << c2[0].ToString()
269 case SpyHashState::CompareResult::kUnequal:
274 return testing::AssertionSuccess();
277 template <typename... T>
279 template <typename U, bool = disjunction<std::is_same<T, U>...>::value>
281 using type = TypeSet<U, T...>;
283 template <typename U>
284 struct Insert<U, true> {
285 using type = TypeSet;
288 template <template <typename...> class C>
289 using apply = C<T...>;
292 template <typename... T>
293 struct MakeTypeSet : TypeSet<> {};
294 template <typename T, typename... Ts>
295 struct MakeTypeSet<T, Ts...> : MakeTypeSet<Ts...>::template Insert<T>::type {};
297 template <typename... T>
298 using VariantForTypes = typename MakeTypeSet<
299 const typename std::decay<T>::type*...>::template apply<absl::variant>;
301 template <typename Container>
302 struct ContainerAsVector {
303 using V = absl::variant<const typename Container::value_type*>;
304 using Out = std::vector<V>;
306 static Out Do(const Container& values) {
308 for (const auto& v : values) out.push_back(&v);
313 template <typename... T>
314 struct ContainerAsVector<std::tuple<T...>> {
315 using V = VariantForTypes<T...>;
316 using Out = std::vector<V>;
318 template <size_t... I>
319 static Out DoImpl(const std::tuple<T...>& tuple, absl::index_sequence<I...>) {
320 return Out{&std::get<I>(tuple)...};
323 static Out Do(const std::tuple<T...>& values) {
324 return DoImpl(values, absl::index_sequence_for<T...>());
329 struct ContainerAsVector<std::tuple<>> {
330 static std::vector<VariantForTypes<int>> Do(std::tuple<>) { return {}; }
333 struct DefaultEquals {
334 template <typename T, typename U>
335 bool operator()(const T& t, const U& u) const {
340 } // namespace hash_internal
342 template <int&..., typename Container>
343 ABSL_MUST_USE_RESULT testing::AssertionResult
344 VerifyTypeImplementsAbslHashCorrectly(const Container& values) {
345 return hash_internal::VerifyTypeImplementsAbslHashCorrectly(
346 hash_internal::ContainerAsVector<Container>::Do(values),
347 hash_internal::DefaultEquals{});
350 template <int&..., typename Container, typename Eq>
351 ABSL_MUST_USE_RESULT testing::AssertionResult
352 VerifyTypeImplementsAbslHashCorrectly(const Container& values, Eq equals) {
353 return hash_internal::VerifyTypeImplementsAbslHashCorrectly(
354 hash_internal::ContainerAsVector<Container>::Do(values), equals);
357 template <int&..., typename T>
358 ABSL_MUST_USE_RESULT testing::AssertionResult
359 VerifyTypeImplementsAbslHashCorrectly(std::initializer_list<T> values) {
360 return hash_internal::VerifyTypeImplementsAbslHashCorrectly(
361 hash_internal::ContainerAsVector<std::initializer_list<T>>::Do(values),
362 hash_internal::DefaultEquals{});
365 template <int&..., typename T, typename Eq>
366 ABSL_MUST_USE_RESULT testing::AssertionResult
367 VerifyTypeImplementsAbslHashCorrectly(std::initializer_list<T> values,
369 return hash_internal::VerifyTypeImplementsAbslHashCorrectly(
370 hash_internal::ContainerAsVector<std::initializer_list<T>>::Do(values),
376 #endif // ABSL_HASH_HASH_TESTING_H_